This invention relates to a method for purifying sodium sulfate solutions of organic and tungsten in order that the sodium sulfate solution can be further processed by ion membrane technology to recover reagent materials.
In the processing of tungsten, tungsten is extracted from sodium tungstate solutions in a liquid-liquid extraction system. In this type of system, tungsten is extracted from a sodium tungstate solution by an organic extracting agent dissolved in a solubilizer. Sodium sulfate solutions are generated as raffinates from the operation of this system. These solutions present a waste removal problem. These solutions can be processed by ion membrane technology to recover sodium hydroxide and sulfuric acid which are usable products. This process avoids production of a waste stream. In ion membrane technology, a cell using ion exchange membranes is used. This cell is a critical part of the process and requires the use of purified solutions since any ion above monovalent contaminates the membranes and renders them inoperative. Some impurities in these solutions are tungsten and residual organic from the liquid-liquid extraction system. One typical organic system makes use of amines as the extracting agent and one or more commercial aromatic solvents. In ion membrane processing, tungsten in the sodium sulfate precipitates and plugs the membranes. Organics in the sodium sulfate solutions dissolve the membranes.
It would be advantageous therefore to purify these solutions of tungsten and organics so that they can be processed to recover usable materials.